Compressed gas supply unit, compressed gas supply apparatus and control method of said unit and said apparatus

ABSTRACT

A compressed gas supply unit includes compressors. Gas discharged from the compressors is stored in a storage tank and then supplied to a gas recipient. The pressure of the storage tank, the operation temperature and the power consumption of each compressor, and the temperature around the compressors are sent to a controller and a monitoring device. A determination unit of the controller determines the presence or absence of the abnormality of the compressor from a difference between the operation temperature of the compressor and the temperature around the compressors. An effective load calculation unit calculates the effective load of each compressor from the power consumption of the compressor and the pressure of the storage tank. The controller controls the compressors based on the calculated effective load such that the loads of the compressors are equalized. An estimation unit estimates maintenance timing from the effective load.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressed gas supply unit whichincludes a plurality of compressors and allows the energy-savingoperation of the compressors and saving of a maintenance cost, acompressed gas supply apparatus, and a control method of the unit andthe apparatus.

2. Description of the Related Art

There is known a compressed gas supply unit which includes a pluralityof compressors and supplies compressed gas to a gas recipient whilecontrolling the number of compressors under operating conditionaccording to a demand. In such a compressed gas supply unit, energysaving is achieved by minimizing the number of compressors underoperating condition. Japanese Patent Application Laid-open No.2010-190197 discloses a compressed gas supply unit which includes ashared storage tank which stores gas discharged from a plurality ofcompressor and a pressure sensor which detects the internal pressure ofthe storage tank, grasps a change in the amount of consumed gas usingthe internal pressure of the storage tank, and controls the number ofcompressors under operating condition according to the detected value ofthe pressure sensor.

Japanese Patent Application Laid-open No. 2010-53733 discloses that, ina compressed gas supply unit having a plurality of air compressors, thesurplus of the ability of each air compressor is calculated from a powerconsumption amount measured in each air compressor under operatingcondition in the control of the number of operated compressors. Inaddition, Japanese Patent Application Laid-open No. 2003-91313 disclosesa remote monitoring system which remotely monitors the operation of aplurality of compressors disposed at remote sites. In the remotemonitoring system, a server of a server-client system is provided in aremote monitoring center, and operation information on the compressorsseparately disposed in a plurality of client plants and the like isdownloaded into the server via the Internet or a public network.

Japanese Patent Application Laid-open No. 2008-258935 discloses a remotemonitoring system in which a plurality of compressors are connected to apersonal computer with a LAN (wired) cable and the operating states ofthe plurality of compressors are monitored using the personal computer.

Although Japanese Patent Application Laid-open No. 2010-53733 disclosesthat the surplus of the ability of each compressor is calculated fromthe power consumption of each compressor, the pressure on the dischargeside of the compressor also influences the power consumption of thecompressor, and hence it is not possible to accurately calculate thesurplus of the compressor only from the power consumption of thecompressor. That is, with the recent prevalence of an inverter, the loadfluctuation of the compressor is no longer raster. In addition, thepower efficiency of the compressor changes depending on the way tooperate the compressor. For example, the power efficiency of thecompressor in an unloaded operation is lowered.

In the system in which the compressor provided in the client plant andthe personal computer provided in the monitoring center or the like areconnected with the LAN cable as the remote monitoring system of acompressed gas supply apparatus, information on other clients may beleaked out of the LAN cable, and hence the system has a securityproblem. In addition, the system requires a construction cost forproviding a network line to the compressor.

In the compressed gas supply unit, energy saving can be achieved by thecombined use of an operation in which a plurality of compressors areoperated with equal loads and control of the number of compressors underoperating condition. In addition, with the equal load operation, it ispossible to eliminate an irregularity in the maintenance timing of thecompressor and reduce the maintenance frequency of the entire compressedgas supply unit to thereby save a maintenance cost and improve theutilization rate of the compressed gas supply unit.

SUMMARY OF THE INVENTION

In view of the problem of the conventional art described above, a firstobject of the present invention is to provide a compressed gas supplyunit including a plurality of compressors which allows an equal loadoperation of the plurality of compressors while monitoring the operatingstate of each compressor and achieves energy saving and saving of amaintenance cost by using the equal load operation and control of thenumber of compressors under operating condition in combination. A secondobject of the present invention is to realize a low-cost remote controlunit without any security problem in a case where a plurality of thecompressed gas supply units disposed at positions apart from each otherare remotely controlled.

A compressed gas supply unit of a first aspect of the present invention(hereinafter referred to as “an apparatus of a first aspect of thepresent invention”) is a compressed gas supply unit including aplurality of compressors, a storage tank which stores discharged gas ofthe compressors, a compressed gas supply pipe which supplies compressedgas to a gas recipient from the storage tank, and a pressure sensorwhich detects a pressure of the storage tank, the compressed gas supplyunit controlling an operation of each of the compressors based on adetected value of the pressure sensor, and including an operating stateamount sensor which detects an operating state amount of the compressor,a power sensor which detects a power consumption of each compressor, anda controller which controls the operation of each compressor.

The controller includes a determination unit which determines that thecompressor is abnormal when the detected value of the operation stateamount sensor exceeds a threshold, an effective load calculation unitwhich calculates an effective load of each compressor from the detectedvalues of the power sensor and the pressure sensor, and an estimationunit which estimates a maintenance timing of each compressor from anaverage value of the calculated effective load in an operation time. Theoperation time may be, e.g., the operation time of the compressed gassupply unit after the previous maintenance, but is not particularlylimited thereto.

The determination unit determines the presence or absence of theabnormality of each compressor, and the operation of each compressor iscontrolled based on the effective load of each compressor calculated bythe effective load calculation unit such that the loads of thecompressors are equalized. In addition, the maintenance is executedbased on the maintenance timing estimated by the estimation unit.

The effective load calculation unit detects the power consumption ofeach compressor and the internal pressure of the storage tank, andcalculates the effective load of each compressor from the detectedvalues. The effective load of the compressor is influenced not only bythe power consumption of the compressor, but also by the internalpressure of the storage tank. Consequently, both of the powerconsumption of the compressor and the internal pressure of the storagetank are detected and the effective load of each compressor iscalculated from the two detected values, and hence it is possible toaccurately calculate the effective load. Next, the average value of thecalculated effective load in the operation time is calculated and themaintenance timing is estimated from the foregoing average value, andhence it is possible to estimate the accurate maintenance timing.

Thus, since the equal load operation of the compressors is performedbased on the calculated effective load, the energy saving of thecompressed gas supply unit is made possible by the combined use of theequal load operation and control of the number of compressors underoperating condition. In addition, with the equal load operation, it ispossible to eliminate an irregularity in the maintenance timing of thecompressor and reduce the maintenance frequency of the entire compressedgas supply unit. As a result, it is possible to save the maintenancecost and also improve the utilization rate of the compressed gas supplyunit. Further, with the estimation unit, it is possible to accuratelyestimate the maintenance timing of the compressor.

The effective load calculation unit may be a unit which determines acorrelation map of the power sensor, the pressure sensor, and theeffective load from a pre-measured value and determines the effectiveload of the compressor from the correlation map. With this, even in acase where at least a part of the compressors is in an unloadedoperation, which is inefficient in power, or an inverter is incorporatedinto the compressor, it is possible to accurately grasp the effectiveload of the compressor, whereby it becomes possible to perform controlof the optimum and minimum number of compressors and achieve the energysaving.

The operation state amount sensor may include a first temperature sensorwhich detects an air temperature around the compressors, and a secondtemperature sensor which detects an operation temperature of eachcompressor, and the determination unit of the controller may be a unitwhich determines that the compressor is abnormal when a differencebetween the detected values of the first temperature sensor and thesecond temperature sensor exceeds a threshold. The operation temperatureof the compressor is, e.g., the temperature of the discharged gas or adischarge path, or the temperature of a partition forming a compressionchamber. With this, it is possible to eliminate the influence of the airtemperature around the compressors exerted on the operation temperatureof the compressor and accurately grasp the presence or absence of theabnormality of the compressor. In addition, since the temperature sensoris used, it is possible to make the apparatus configuration relativelysimple and make its cost lower.

The operation state amount sensor may be a second pressure sensor whichdetects a pressure of the discharged gas of the compressor, and thedetermination unit of the controller may be a unit which determines thatthe compressor is abnormal when a difference between the detected valuesof the pressure sensor and the second pressure sensor exceeds athreshold. With this, it becomes possible to perform the accuratedetermination without the influence of the internal pressure of thestorage tank.

The apparatus of the first aspect of the present invention may includean inverter capable of controlling the RPM of the compressor, and thecontroller may control the operation of the compressor via the inverter.With this, it is possible to individually control the loads of thecompressors, and hence the equal load operation is facilitated.

A compressed gas supply apparatus of a second aspect of the presentinvention (hereinafter referred to as “an apparatus of a second aspectof the present invention”) includes a plurality of the compressed gassupply units disposed at positions apart from each other and a centralcontroller which can perform data communication by means of a wirelessaccess system with the plurality of compressed gas supply units. Thecentral controller includes a storage unit which stores detected valuedata received from the plurality of compressed gas supply units, and acorrection unit which corrects the threshold from the detected valuedata accumulated in the storage unit and a result of an actualabnormality occurrence of the compressor, and controls each of thecompressed gas supply units based on the corrected threshold.

The result of the actual abnormality occurrence of the compressormentioned herein means, e.g., data obtained when an operator visuallyidentifies the abnormality, and the operator inputs the data such as thethreshold or the like at the time of the identification in the centralcontroller. According to the apparatus of the second aspect of thepresent invention, by successively correcting the threshold inconjunction with watching the result of the actual abnormalityoccurrence of the compressor, it is possible to accurately determine thepresence or absence of the abnormality of the compressor. In addition,the presence or absence of the abnormality of the compressor isdetermined based on a population of the high detected values collectedfrom the plurality of compressed gas supply units, and hence it becomespossible to perform the accurate determination.

A compressed gas supply apparatus of the present invention (hereinafterreferred to as “an apparatus of a third aspect of the presentinvention”) includes a plurality of the compressed gas-supply unitsdisposed at positions apart from each other, a central controller whichremotely controls the operation of the plurality of compressed gassupply units, a connection pipe which connects the compressed gas supplypipes of the plurality of compressed gas supply units, and an on-offvalve provided in the connection pipe, and the central controllerremotely controls the on-off valve based on a detected value of apressure of a storage tank received from each of the plurality ofcompressed gas supply units.

According to the apparatus of the third aspect of the present invention,it is possible to supply the compressed gas to a plurality of gasrecipients via the connection pipe from one compressed gas supply unit.In addition, it is possible to send the compressed gas to the pluralityof gas recipients in conjunction with monitoring the storage state ofthe compressed gas in the storage tank of each compressed gas supplyunit by means of the central controller, whereby it is possible toefficiently utilize the compressed gas produced by the plurality ofcompressed gas supply units.

A control method of a compressed gas supply unit of the presentinvention (hereinafter referred to as “a method of a first aspect of thepresent invention”) is for a compressed gas supply unit whichtemporarily stores discharged gas out of a plurality of compressors in astorage tank, supplies compressed gas to a gas recipient from thestorage tank, detects an internal pressure of the storage tank, andcontrols an operation of each of the compressors based on a detectedvalue of the pressure.

A first step of the method of the first aspect of the present inventiondetects an operating state amount of each of the plurality ofcompressors and determines that the compressor is abnormal when thedetected value exceeds a threshold. As the operation state amount, forexample, the air temperature around the compressors and the operationtemperature of each compressor are detected and it is determined thatthe compressor is abnormal when a difference between these detectedtemperature values exceeds a threshold. With this, it is possible toeliminate the influence of the air temperature around the compressorsexerted on the compressor and accurately grasp the presence or absenceof the abnormality of the compressor. In addition, since the temperaturesensor is used, it is possible to make the apparatus configurationrelatively simple and make its cost lower. As described above, theoperation temperature of the compressor is, e.g., the temperature of thedischarged gas or the discharge path, or the temperature of thepartition forming the compression chamber.

As another step, the internal pressure of the storage tank and apressure of the discharged gas of each compressor may be detected and itmay be determined that the compressor is abnormal when a differencebetween these detected pressure values exceeds a threshold. With this,it becomes possible to perform the accurate determination without theinfluence of the internal pressure of the storage tank. In addition,since the internal pressure of the storage tank and the pressure of thedischarge gas of each compressor are detected, it becomes possible toperform the accurate determination.

A second step detects a power consumption of each compressor and theinternal pressure of the storage tank, and calculates an effective loadof each compressor from these detected values. The effective load of thecompressor is influenced not only by the power consumption of thecompressor, but also by the internal pressure of the storage tank.Consequently, both of the power consumption of the compressor and theinternal pressure of the storage tank are detected and the effectiveload of each compressor is calculated from the two detected values sothat it is possible to accurately calculate the effective load. Next, anaverage value of the calculated effective load in an operation time iscalculated and maintenance timing is estimated from the average value.With this, it becomes possible to estimate the accurate maintenancetiming. The operation time may be, e.g., the operation time of thecompressed gas supply unit after the previous maintenance, but is notparticularly limited thereto.

A third step controls the operation of each compressor based on theeffective load of each compressor calculated in the second step suchthat the loads of the compressors are equalized. The energy saving ofthe compressed gas supply unit is made possible by the combined use ofthe equal load operation and the control of the number of compressorsunder operating condition. In addition, with the equal load operation,it is possible to eliminate the irregularity in the maintenance timingof the compressor and reduce the maintenance frequency of the entirecompressed gas supply unit, whereby it is possible to save themaintenance cost and improve the utilization rate of the compressed gassupply unit.

Note that, when the compressor is constituted of a multi-stagecompressor, the first step may detect the operation temperature or thepressure of the discharged gas of the compressors other than the finalhigh-pressure stage compressor. When an abrasion is caused in thedischarge path of a low-pressure side compressor by the operation of themulti-stage compressor, high-temperature and high-pressure gas of ahigh-pressure side compressor flows backward to the low-pressure sidecompressor and the temperature of the discharge path and the pressure ofthe discharge gas of the low-pressure side compressor are increased.Consequently, by detecting the temperature of the discharge path or thepressure of the discharge gas of the low-pressure side compressor, it ispossible to detect the presence or absence of the backward flow of thehigh-temperature and high-pressure gas. With this, it is possible toaccurately grasp the progress of fatigue of the compressor, and hence itis possible to properly estimate the maintenance timing.

A control method of a compressed gas supply apparatus of the presentinvention (hereinafter referred to as “a method of a second aspect ofthe present invention”) is for a compressed gas supply apparatus whichincludes a plurality of the compressed gas supply units disposed atpositions apart from each other and a central controller which canperform data communication by means of a wireless access system with thecompressed gas supply units.

First to third steps of the method of the second aspect of the presentinvention are the same as the first to third steps of the method of thefirst aspect of the present invention. Fourth to sixth steps of themethod of the second aspect of the present invention include the fourthstep of transmitting detected value data to the central controller fromthe compressed gas supply units, the fifth step of causing a storageunit of the central controller to store the detected value data of thecompressed gas supply units, and the sixth step of correcting thethreshold from the detected value data accumulated in the storage unitand a result of an actual abnormality occurrence of the compressor andcontrolling each compressed gas supply unit based on the correctedthreshold.

The result of the actual abnormality occurrence of the compressormentioned herein means, e.g., data obtained when the operator visuallyidentifies the abnormality, and the operator inputs the data such as thethreshold or the like at the time of the identification in the centralcontroller. By successively correcting the threshold from the result ofthe actual abnormality occurrence of the compressor, it is possible todetermine the presence or absence of the abnormality of the compressorfurther accurately. In addition, the presence or absence of theabnormality of the compressor is determined based on the population ofthe high detected values collected from the plurality of compressed gassupply units, and hence it becomes possible to perform the accuratedetermination.

According to the apparatus of the first aspect of the present inventionand the method of the first aspect of the present invention, since it ispossible to accurately grasp the abnormality of the compressor duringthe operation and perform the operation in which the loads of thecompressors are equalized, the combined use of the equal load operationand the control of the number of operated compressors allows energysaving, and can reduce the maintenance frequency and save themaintenance cost. In addition, according to the apparatus of the secondaspect of the present invention and the method of the second aspect ofthe present invention, in addition to the operation and effect describedabove, by successively correcting the threshold related to thedifference between the air temperature around the compressors and theoperation temperature of the compressor, it is possible to determine thepresence or absence of the abnormality of the compressor furtheraccurately. Additionally, according to the apparatus of the third aspectof the present invention, it is possible to efficiently supply thecompressed gas produced by the plurality of compressed gas supply unitsto a plurality of gas recipients on the demands thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a compressed gas-supply unit according toa first embodiment of each of an apparatus of a first aspect of thepresent invention and a method of a first aspect of the presentinvention;

FIG. 2 is a correlation map for determining the effective load of acompressor in the first embodiment;

FIG. 3 is a partial system diagram of a compressed gas supply unitaccording to a second embodiment of each of the apparatus of the firstaspect of the present invention and the method of the first aspect ofthe present invention;

FIG. 4 is a system diagram of a compressed gas supply apparatusaccording to an embodiment of each of an apparatus of a second aspect ofthe present invention and a method of a second aspect of the presentinvention; and

FIG. 5 is a system diagram of a compressed gas supply apparatusaccording to an embodiment of an apparatus of a third aspect of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described in detail by usingembodiments shown in the drawings. Note that the scope of the presentinvention is not limited to dimensions, materials, shapes, and relativearrangements of constituent parts described in the embodiments unlessspecifically described.

First Embodiment

A first embodiment of each of an apparatus of a first aspect of thepresent invention and a method of a first aspect of the presentinvention will be described with reference to FIGS. 1 and 2. Acompressed gas supply unit 10A of the present embodiment includes onestorage tank 12 and four compressors 14 a to 14 d. Discharge paths 16 ato 16 d of the individual compressors are connected to a main supplypipe 18, and the main supply pipe 18 is connected to the storage tank12. Gas discharged from each compressor flows through the main supplypipe 18 and is stored in the storage tank 12.

The individual compressors are provided with drive motors 20 a to 20 dand inverters 22 a to 22 d which can control the RPMs of the drivemotors steplessly. With this, the RPMs of the individual motors can beindividually controlled. Temperature sensors 24 a to 24 d which detectthe temperatures of compressed gas are provided on the partitions ofcompression chambers of the individual compressors. The compressors areprovided with power sensors 26 a to 26 d which detect power consumptionsof the drive motors 20 a to 20 d.

The storage tank 12 is provided with a pressure sensor 28 which detectsan internal pressure in the storage tank 12. A temperature sensor 32which detects an air temperature around the compressors is provided inthe vicinity of the compressors 14 a to 14 d. Detection signals of thetemperature sensors 24 a to 24 d, the power sensors 26 a to 26 d, thepressure sensor 28, and the temperature sensor 32 are sent to acontroller 34 provided in a monitoring room or the like.

The controller 34 opens or closes an on-off valve 39 provided in acompressed gas supply pipe 38 to supply compressed gas to a gasrecipient 30 in conjunction with monitoring the detected value of thepressure sensor 28. The controller 34 has a determination unit 35, aneffective load calculation unit 36, and an estimation unit 37. Thedetermination unit 35 determines the presence or absence of theabnormality of each of the compressors 14 a to 14 d from a difference ΔTbetween the detected value of the temperature sensor 32 and the detectedvalue of each of the temperature sensors 24 a to 24 d. That is, when thedifference ΔT exceeds a threshold ΔTs, the determination unit 35determines that the state of the compressor is abnormal.

The effective load calculation unit 36 calculates the effective load ofeach of the compressors 14 a to 14 d from the detected values of thepressure sensor 28 and the power sensors 26 a to 26 d. FIG. 2 is a mapshowing the correlation of the power consumption of each of thecompressors 14 a to 14 d, the internal pressure of the storage tank 12,and the effective load of each of the compressors 14 a to 14 d which aredetermined from pre-measured test data by using the compressor havingthe same type and capacity as those of each of the compressors 14 a to14 d. The effective load of each of the compressors 14 a to 14 d iscalculated from the detected values of the pressure sensor 28 and thepower sensors 26 a to 26 d by using the map.

The estimation unit 37 estimates the maintenance timing of eachcompressor from the average value of the effective load calculated inthe effective load calculation unit 36 in an operation time. In thepresent embodiment, the operation time is assumed to be the operationtime of the compressed gas supply unit 10A from the time point of startof the operation after the previous maintenance to the time point of thecalculation. However, in the present invention, the operation time isnot limited thereto and other times may be set as the operation time.The average value is calculated with the stop time of each compressorincluded, and the average value is calculated for each compressor.Alternatively, the average value of the four compressors may also becalculated instead of calculating the average value for each compressor.

A monitoring device 40 is provided in the monitoring room or the like.To the monitoring device 40, the detection signal of each sensor is sentfrom the controller 34, and the determination result of thedetermination unit 35, the effective load of each compressor calculatedin the effective load calculation unit 36, and the signal indicative ofthe next maintenance timing estimated in the estimation unit 37 are alsosent. The monitoring device 40 includes a display unit 42 and an alarmdevice 44. The display unit 42 displays the detected value of eachsensor, the determination result of the determination unit 35, theeffective load calculated in the effective load calculation unit 36, andthe next maintenance timing estimated in the estimation unit 37.

The controller 34 performs an operation in which control of the numberof compressors which minimizes the number of compressors under operatingcondition with respect to the load of the compressed gas supply unit 10Aand an equal load operation which controls the inverters 22 a to 22 d ofthe individual compressors 14 a to 14 d based on the effective loads ofthe individual compressors calculated in the effective load calculationunit 36 such that the loads of the compressors 14 a to 14 d areequalized, are used in combination. In addition, when the determinationresult of the determination unit 35 indicates the presence of theabnormality, the alarm device 44 issues an alarm. Further, an operatorperforms the maintenance based on the next maintenance timing displayedin the display unit 42.

According to the present embodiment, since the determination unit 35 ofthe controller 34 determines the presence or absence of the abnormalityof each compressor based on the difference ΔT between the temperaturearound the compressors 14 a to 14 d and the compressed gas temperatureof the compression chamber of each of the compressors 14 a to 14 d, itbecomes possible to perform accurate abnormality determination withoutthe influence of the air temperature. In addition, since the temperaturesensor is used, it is possible to make the apparatus configurationrelatively simple and make its cost lower.

In addition, since the effective load of each of the compressors 14 a to14 d is calculated from the correlation map shown in FIG. 2 in theeffective load calculation unit 36 of the controller 34, it is possibleto calculate the accurate effective load. Further, since the controller34 performs the operation in which the control of the number ofcompressors and the equal load operation are used in combination, energysaving is made possible. Furthermore, with the equal load operation, itis possible to eliminate an irregularity in the maintenance timing ofthe compressor and reduce the maintenance frequency of the entirecompressed gas supply unit, whereby it is possible to save themaintenance cost and improve the utilization rate of the compressed gassupply unit.

In addition, since there are provided the inverters 22 a to 22 d whichcan control the RPMs of the compressors 14 a to 14 d individually, theload control of each compressor is facilitated. In the presentembodiment, although the controller 34 and the monitoring device 40 areseparately provided, an integrated monitoring controller having thesefunctions may also be used instead.

Although the effective loads of the compressors 14 a to 14 d arecalculated from the detected values of the pressure sensor 28 and thepower sensors 26 a to 26 d in the present embodiment, the pressure ofthe discharged gas of each of the compressors 14 a to 14 d may bedetected instead, and when the difference between the detected value ofthe pressure sensor 28 and the detected value of the pressure of thedischarged gas of the compressor exceeds a threshold, it may bedetermined that the corresponding compressor is abnormal. With this, itbecomes possible to perform accurate determination without the influenceof the internal pressure of the storage tank 12.

Second Embodiment

Next, a second embodiment of each of the apparatus of the first aspectof the present invention and the method of the first aspect of thepresent invention will be described with reference to FIG. 3. Atwo-stage compressor 50 constituting a compressed gas supply unit 10B ofthe present embodiment includes a low-pressure side compressor 52 and ahigh-pressure side compressor 54. That is, the low-pressure sidecompressor 52 and the high-pressure side compressor 54 are driven by ashared rotating shaft 58, and the rotating shaft 58 is driven by a drivemotor 56. Gas discharged from the low-pressure side compressor 52 issupplied to the high-pressure side compressor 54 via an intermediatedischarge path 60, further compressed in the high-pressure sidecompressor 54, and sent to the storage tank (not shown). The RPM of thedrive motor 56 can be steplessly adjusted by an inverter 62.

The intermediate discharge path 60 is provided with a temperature sensor64 which detects the temperature of the intermediate discharge path 60,and the drive motor 56 is provided with a power sensor 66 which detectsthe power consumption of the drive motor 56. The detection signals ofthese sensors are sent to the monitoring device 40, and the inverter 62is controlled by the controller 34. The configuration of the compressedgas supply unit 10B is otherwise the same as that of the firstembodiment.

In the two-stage compressor 50, when an abrasion or the like progressesin a portion constituting the compression chamber, high-pressure air ofthe high-pressure side compressor 54 may flow backward to thelow-pressure side compressor 52 through the intermediate discharge path60. According to the present embodiment, the temperature of theintermediate discharge path 60 is detected as the operation temperatureof the two-stage compressor 50, and hence it is possible to detect thepresence or absence of the backward flow of the high-pressure air. Withthis, it is possible to accurately grasp the progress of fatigue of thetwo-stage compressor 50, and hence it is possible to accurately graspthe maintenance timing of the two-stage compressor 50.

Note that, in the present embodiment as well, instead of the temperatureof the intermediate discharge path 60, the pressure of the discharge airof the intermediate discharge path 60 may be detected, and when thedifference between the pressure of the discharge air and the internalpressure of the storage tank 12 exceeds a threshold, it may bedetermined that the compressor is abnormal. With this, it becomespossible to perform the accurate determination without the influence ofthe internal pressure of the storage tank 12.

Third Embodiment

Next, an embodiment of each of an apparatus of a second aspect of thepresent invention and a method of a second aspect of the presentinvention will be described with reference to FIG. 4. A compressed gassupply apparatus 70 of the present embodiment includes a plurality ofcompressed gas supply units 10A, 10B, and 10C provided at positionsapart from each other and a central control unit 72 which can remotelycontrol the compressed gas supply units. Each of the compressed gassupply units 10A and 10C has the same configuration as that of thecompressed gas supply unit 10A of the first embodiment, and thecompressed gas supply unit 10B has the same configuration as that of thecompressed gas supply unit 10B of the second embodiment.

The compressed gas supply unit 10A and the central control unit 72 areprovided with transmitter-receivers 74 and 80 respectively. Thecompressed gas supply unit 10A and the central control unit 72 canperform data communication therebetween by means of a data communicationnetwork 82 of a wireless access system provided by a cellular phonecarrier. The central control unit 72 and the compressed gas supply unit10B or 10C can also perform the data communication therebetween by meansof the same wireless access system. Data such as detected values and thelike held by the monitoring device 40 of each compressed gas supply unitis sent to the central control unit 72 through the data communicationnetwork 82.

The central control unit 72 has a storage unit 76 and a correction unit78. The detected values of the temperature sensors 24 a to 24 d and 32received from the compressed gas supply units 10A, 10B, and 10C arestored in the storage unit 76. In the correction unit 78, the thresholdΔTs related to the difference ΔT between the detected value of thetemperature sensor 32 and the detected value of each of the temperaturesensors 24 a to 24 d is corrected based on the detected values stored inthe storage unit 76 and the result of the actual abnormality occurrenceof the compressor. The result of the actual abnormality occurrence ofthe compressor mentioned herein means data obtained when the operatorvisually identifies the abnormality, and the operator inputs thethreshold ΔTs at the time of the identification in the central controlunit 72.

The central control unit 72 controls the operation of each compressedgas supply unit based on the successively corrected threshold ΔTs duringthe operation of the compressed gas supply apparatus 70. Note that themonitoring device 40 of each compressed gas supply unit and the centralcontrol unit 72 may be accessed from a cellular phone 84 held by theoperator via the data communication network 82. That is, the operationstate of each compressed gas supply unit may be monitored by receivingdata from the central control unit 72 and the monitoring device 40 ofeach compressed gas supply unit by means of the cellular phone 84.

According to the present embodiment, in addition to the operation andeffect obtained in the first embodiment of each of the method of thefirst aspect of the present invention and the apparatus of the firstaspect of the present invention, by successively correcting thethreshold ΔTs of each compressed gas supply unit in conjunction withwatching the result of the actual abnormality occurrence of thecompressor, it is possible to accurately determine the presence orabsence of the abnormality of the compressor. In addition, the presenceor absence of the abnormality of the compressor is determined based on apopulation of the high detected values collected from the plurality ofcompressed gas supply units, and hence it becomes possible to performthe accurate determination.

Fourth Embodiment

Next, an embodiment of an apparatus of a third aspect of the presentinvention will be described with reference to FIG. 5. A compressed gassupply apparatus 90 of the present embodiment includes two compressedgas supply units 10D and 10E and a central control unit 92 whichcontrols the operation of the compressed gas supply units 10D and 10E.The compressed gas supply unit 10D includes a storage tank 100, fourcompressors 102 a to 102 d, a pressure sensor 104 which detects theinternal pressure of the storage tank 100, and a compressed gas supplypipe 106 which supplies compressed gas in the storage tank 100 to a gasrecipient 108.

The compressed gas supply unit 10E includes a storage tank 110, fourcompressors 112 a to 112 d, a pressure sensor 114 which detects theinternal pressure of the storage tank 110, and a compressed gas supplypipe 116 which supplies the compressed gas in the storage tank 110 to agas recipient 118. Each of the compressed gas supply units 10D and 10Ehas the same configuration as that of the compressed gas supply unit 10Aof FIG. 1. The compressed gas supply pipe 106 and the compressed gassupply pipe 116 are connected to each other by a connection pipe 96. Theconnection pipe 96 is provided with an on-off valve 98.

As in the above embodiment, the data communication can be performedbetween the central control unit 92 and the compressed gas supply unit10D or 10E or the on-off valve 98 by means of data communicationnetworks 94 of the wireless access system.

In the present embodiment, the opening/closing operation of the on-offvalve 98 is controlled by the central control unit 92. For example, in acase where the compressed gas is supplied to the gas recipient 108 andthe internal pressure P₁ of the storage tank 100>the internal pressureP₂ of the storage tank 110 is satisfied, it is possible to supply thecompressed gas in the storage tank 100 to the gas recipient 118 byopening the on-off valve 98. In this manner, it is possible to monitorthe internal pressure P₁ of the storage tank 100 and the internalpressure P₂ of the storage tank 110 by using the central control unit 92to send the compressed gas of the compressed gas-supply unit 10D or 10Eto the gas recipient of the other compressed gas supply apparatus,whereby it is possible to efficiently supply the compressed gas to theplurality of gas recipients 108 and 118.

The present invention allows the energy-saving operation and themaintenance cost reduction of a compressed gas supply unit including aplurality of compressors, and solves a security problem and allowslow-cost remote control in a compressed gas supply apparatus including aplurality of the compressed gas supply units.

What is claimed is:
 1. A compressed gas supply unit comprising aplurality of compressors, a storage tank which stores discharge gas ofthe compressors, a compressed gas supply pipe which supplies compressedgas to a gas recipient from the storage tank, and a pressure sensorwhich detects a pressure of the storage tank, the compressed gas supplyunit controlling an operation of each of the compressors based on adetected value of the pressure sensor, and comprising: an operatingstate amount sensor which detects an operating state amount of thecompressor; a power sensor which detects a power consumption of eachcompressor; and a controller which controls the operation of eachcompressor, wherein the controller comprises a determination unit whichdetermines that the compressor is abnormal when the detected value ofthe operating state amount sensor exceeds a threshold, an effective loadcalculation unit which calculates an effective load of each compressorfrom the detected values of the power sensor and the pressure sensor,and an estimation unit which estimates a maintenance timing of eachcompressor from an average value of the calculated effective load in anoperation time, and the controller controls the operation of eachcompressor based on the calculated effective load of each compressorsuch that loads of the compressors are equalized.
 2. The compressed gassupply unit according to claim 1, wherein the effective load calculationunit for the compressors is a unit which determines a correlation map ofthe power sensor, the pressure sensor, and the effective load from apre-measured value and determines the effective load of the compressorfrom the correlation map.
 3. The compressed gas supply unit according toclaim 1, wherein the operating state amount sensor comprises a firsttemperature sensor which detects an air temperature around thecompressors, and a second temperature sensor which detects an operationtemperature of each compressor, and the determination unit of thecontroller is a unit which determines that the compressor is abnormalwhen a difference between the detected values of the first temperaturesensor and the second temperature sensor exceeds a threshold.
 4. Thecompressed gas supply unit according to claim 1, wherein the operationstate amount sensor is a second pressure sensor which detects a pressureof the discharge gas of the compressor, and the determination unit ofthe controller is a unit which determines that the compressor isabnormal when a difference between the detected values of the pressuresensor and the second pressure sensor exceeds a threshold.
 5. Thecompressed gas supply unit according to claim 1, wherein each compressorcomprises an inverter capable of controlling an RPM, and the controllercontrols the inverter such that loads of the compressors are equalized.6. A compressed gas supply apparatus comprising: a plurality of thecompressed gas supply units according to claim 1 disposed at positionsapart from each other; and a central controller which can perform datacommunication by means of a wireless access system with the plurality ofcompressed gas supply units, wherein the central controller comprises astorage unit which stores detected value data received from theplurality of compressed gas supply units, and a correction unit whichcorrects the threshold from the detected value data accumulated in thestorage unit and a result of an actual abnormality occurrence of thecompressor, and controls each of the compressed gas supply units basedon the corrected threshold.
 7. A compressed gas supply apparatuscomprising: a plurality of the compressed gas supply units according toclaim 1 disposed at positions apart from each other; a centralcontroller which can perform data communication by means of a wirelessaccess system with the plurality of compressed gas supply units; aconnection pipe which connects the compressed gas supply pipes of theplurality of compressed gas supply units; and an on-off valve providedin the connection pipe, wherein the central controller remotely controlsthe on-off valve based on a detected value of a pressure of a storagetank received from each of the plurality of compressed gas-supply units.8. A control method of a compressed gas supply unit which temporarilystores discharged gas of a plurality of compressors in a storage tank,supplies compressed gas to a gas recipient from the storage tank,detects a pressure of the storage tank, and controls an operation ofeach of the compressors based on a detected value of the pressure, thecontrol method comprising: a first step of detecting an operating stateamount of each compressor and determining that the compressor isabnormal when the detected value exceeds a threshold; a second step ofdetecting a power consumption of each compressor and an internalpressure of the storage tank, calculating an effective load of eachcompressor from the detected values, and estimating a maintenance timingof each compressor from an average value of the calculated effectiveload in an operation time; and a third step of controlling the operationof each compressor based on the effective load of each compressorcalculated in the second step such that the effective loads of thecompressors are equalized.
 9. The control method of a compressed gassupply unit according to claim 8, wherein the first step is a step ofdetecting an air temperature around the compressors and an operationtemperature of each compressor and determining that the compressor isabnormal when a difference between these detected temperature valuesexceeds a threshold.
 10. The control method of a compressed gas supplyunit according to claim 8, wherein the first step is a step of detectingthe internal pressure of the storage tank and a pressure of thedischarge gas of each compressor and determining that the compressor isabnormal when a difference between these detected pressure valuesexceeds a threshold.
 11. The control method of a compressed gas supplyunit according to claim 9, wherein each compressor is constituted of amulti-stage compressor, and the operation temperature or the pressure ofthe discharge gas of the compressor is the operation temperature or thepressure of the discharge gas of the compressor other than a finalhigh-pressure stage compressor.
 12. A control method of a compressed gassupply apparatus comprising: a plurality of compressed gas supply unitswhich are disposed at positions apart from each other, temporarily storedischarge gas of a plurality of compressors in a storage tank, supplycompressed gas to a gas recipient from the storage tank, detect apressure of the storage tank, and control an operation of each of thecompressors based on a detected value of the pressure; and a centralcontroller which can perform data communication by means of a wirelessaccess system with the compressed gas supply units, the control methodcomprising: a first step of detecting an operating state amount of eachcompressor and determining that the compressor is abnormal when thedetected value thereof exceeds a threshold; a second step of detecting apower consumption of each compressor and an internal pressure of thestorage tank, calculating an effective load of each compressor from thedetected values, and estimating a maintenance timing of each compressorfrom an average value of the calculated effective load in an operationtime; a third step of controlling the operation of each compressor basedon the effective load of each compressor calculated in the second stepsuch that the effective loads of the compressors are equalized; a fourthstep of transmitting detected value data to the central controller fromthe compressed gas supply units; a fifth step of causing a storage unitof the central controller to store the detected value data of thecompressed gas supply units; and a sixth step of correcting thethreshold from the detected value data accumulated in the storage unitand a result of an actual abnormality occurrence of the compressor andcontrolling each compressed gas supply unit based on the correctedthreshold.